Trend analysis in hydrological time series of the Bauru Aquifer System (BAS)

Abstract

The Bauru Aquifer System (BAS) is a vital water source for a vast and densely populated region of Brazil, covering the states of São Paulo, Minas Gerais, Paraná, and Mato Grosso do Sul. Given the increasing water demand and the scarcity of studies on the long-term behavior of this aquifer, this study aimed to analyze temporal trends in potentiometric level, precipitation, and recharge in the BAS. To accomplish this, data from 29 monitoring wells of the Integrated Groundwater Monitoring Network (RIMAS/SGB) and precipitation data from the CHIRPS product were used. Statistical analysis was performed using the non-parametric Mann–Kendall test and Sen’s slope estimator. The results revealed a statistically significant declining trend in the potentiometric level in 25 of the 29 wells analyzed, with drawdown rates ranging from -0.07 to -1.23 m/year. In contrast, the analysis of precipitation data showed no significant trend across most of the study area. The discrepancy between stable precipitation and the marked decline in groundwater levels suggests that the potentiometric-level drawdown in the BAS is the result of a combination of factors, including increased groundwater exploitation and potential changes in aquifer recharge behavior influenced by shifts in rainfall distribution. These findings reinforce the need for continuous monitoring and sustainable management strategies to ensure water security in the region.